Technical Field
The present disclosure relates to a three-dimensional measurement device configured to execute three-dimensional measurement.
Description of Related Art
In general, when electronic components are to be mounted on a printed circuit board, solder paste is printed on a predetermined electrode pattern provided on the printed circuit board. The electronic components are then temporarily fastened on the printed circuit board by taking advantage of the viscosity of the solder paste. The printed circuit board is subsequently introduced into a reflow furnace and is subjected to a predetermined reflow process to achieve soldering. Recently there has been a need to inspect the printing condition of solder paste in a stage prior to introduction into the reflow furnace. A three-dimensional measurement device may be used for this inspection.
Various contactless three-dimensional measurement devices using light have been proposed lately. For example, three-dimensional measurement devices employing the phase shift method are known well.
A known three-dimensional measurement device using the phase shift method includes, for example, a moving mechanism configured to move a measured object, an irradiation device configured to irradiate the measured object with striped pattern light, and an imaging device configured to take an image of the measured object irradiated with the pattern light (as described in, for example, Patent Literature 1). The imaging device is comprised of, for example, a lens and an imaging element.
This three-dimensional measurement device obtains a plurality of image data having different light intensity distributions on the measured object that are different from each other by every predetermined phase of the pattern light, by relatively moving the measured object to a measurement head comprised of the irradiation device and the imaging device. Three-dimensional measurement of the measured object is then executed by the phase shift method, based on the plurality of image data.
For example, when four different image data obtained have light intensity distributions on a measured object that are different from one another by the phase of 90 degrees each of the pattern light, luminance values I0, I1, I2 and I3 of the four different image data at a predetermined coordinate position on the measured object are expressed by Expressions (1), (2), (3) and (4) given below:I0=αsin θ+β  (1)I1=αsin(θ+90°)+β=αcos θ+β  (2)I2=αsin(θ+180°)+β=−αsin θ+β  (3)I3=αsin(θ+270°)+β=−αcos θ+β  (4)where α represents a gain, β represents an offset, and θ represents a phase of pattern light.
Expression (5) given below is derived by solving Expressions (1), (2), (3) and (4) for the phase θ:θ=tan−1{(I0-I2)/(I1-I3)}  (5)A height (Z) at each coordinates (X,Y) on the measured object can be determined by using the phase θ calculated as described above, based on the principle of triangulation.
When a measured object such as a printed circuit board has a warpage or the like, however, there is a difficulty in placing the entire measured object within a focusing range. This may cause partly out-of-focus image data to be obtained and is thus likely to decrease the measurement accuracy.
A recently proposed technique relatively moves and adjusts a measurement head comprised of an irradiation device and an imaging device in a height direction (Z-axis direction), such as to maintain a constant interval between a measured object and the imaging device (as described in, for example, Patent Literature 2).